Turbo charged engines utilize a Charge Air Cooler (CAC) to cool compressed air from the turbocharger, before it enters the engine. Ambient air from outside the vehicle travels across the CAC to cool intake air passing through the inside of the CAC. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. When the intake air includes recirculated exhaust gasses, the condensate can become acidic and corrode the CAC housing. The corrosion can lead to leaks between the air charge, the atmosphere, and possibly the coolant in the case of water-to-air coolers. Condensate may collect at the bottom of the CAC, and then be drawn into the engine at once during acceleration (or tip-in) increasing the chance of engine misfire.
Other attempts to address condensate formation include restricting intake air travelling through the CAC or restricting ambient air flow to the CAC. One example approach is shown by Craig et al. in U.S. Pat. No. 6,408,831. Therein, the intake air temperature is controlled by an ambient air flow restriction system and an intake air flow restriction system. A controller defines the position of these restriction devices and is connected to a plurality of sensors which measure different variables such as ambient air and intake air temperatures.
However, the inventors herein have recognized potential issues with such systems. Specifically, the above control of restriction devices in response to intake or ambient air temperature may reduce the overall level of condensate, while potentially increasing the concentration of acid in the condensate that does form. Maintaining temperatures at a certain level such that condensate formation is low may result in sustaining a flow restriction for a period of time. This keeps the CAC effectiveness at one level, causing the dew point to hover at one location in the CAC. This may result in an increased acid concentration at one location, actually creating a higher corrosion risk. This is because the corrosion risk is most severe at the location in the CAC where the charge air temperature drops below the dew point and water begins to condense, creating the highly concentrated water and acid solution, especially if the level of condensate is kept low.
In one example, the issues described above may be addressed by a method for controlling a vehicle engine cooling fan, comprising: adjusting fan rotation speed or rotation direction in response to a condensate location in a charge air cooler remaining within a positional range for greater than a threshold duration. The fan may be adjusted to move the condensate location toward an inlet of the charge air cooler (e.g., increase rotation speed) during a first set of conditions, and may be adjusted to move the condensate location toward an outlet of the charge air cooler (e.g., decrease rotation speed or turn rotation off) during a second, different, set of conditions. In this way, by moving the location of the condensate formation in the charge air cooler, e.g., back and forth within the charge air cooler, if the location becomes stagnant, it is possible to reduce corrosion risk at any given location from the inlet to the outlet of the charge air cooler, as one example.
In addition to condensate formation, the engine cooling fan may be adjusted in response to engine cooling parameters, outside weather conditions, and non-driven vehicle conditions, such as deceleration. Adjustment of the engine cooling fan may be coordinated with grille shutter operation in order to optimize condensate control, as well as engine cooling and fuel economy. For example, the inventors herein have identified approaches that enable the engine cooling fan and grille shutters to still be adjusted in a way that improves fuel economy (by reducing drag), but that also maintains engine coolant temperature control to avoid over temperature and reduces condensate formation.
Specifically, it may be possible to pre-cool the engine coolant during a deceleration by opening the grille shutters and turning on the engine cooling fan so that a subsequent acceleration operation can maintain the grille shutters closed for a longer duration, without resulting in over temperature conditions of the coolant. However, such pre-cooling operation may also exacerbate the potential for condensate formation, as the charge air cooler may be cooled to a greater extent. Therefore, in one example, the engine cooling fan speed or direction may be changed responsive to condensate formation during the deceleration condition.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.